Diurnal and seasonal variations of the steady state loss coefficient in the D region

Abstract

A study was made of the steady state loss coefficient ψ (= q/N²) deduced for quiet periods from previously published electron density height data. Near 75 km, ψ was found to remain fairly constant with diurnal changes of the solar zenith angle χ, while above 77 km, ψ decreased with decreasing χ. Since a seasonal variation in ψ was not clearly evident, observational data selected from more than 4 years of partial reflection observations at Ottawa, were analyzed for quiet intervals at the minimum solar zenith angle (χ≡68°) that could be followed in all seasons. This study revealed that for heights above 76 km, ψ was a minimum in winter and a maximum in summer. Near 75 km neither a seasonal nor a diurnal variation was found, and ψ remained fairly constant near 2 × 10−5 cm³ s−1. These results are interpreted as indicating that for heights above 77 km, (1) as χ decreases, there is a gradual decrease in the number density of the larger hydrated positive ions thought to be responsible for the high ψ values and (2) the existence of these larger hydrate positive ions is temperature dependent, such that they are absent in the warm winter mesosphere and present in the cool summer mesosphere.